In the aftermath of the English Civil War, Oliver Cromwell, the head of the new British government, returned to the pragmatic foreign policy practiced during the days of Elizabeth I. Cromwell's oppurtunism led, in 1654, to the Anglo-Spanish War, ending the civil war's confinement of British conflicts to the British Isles and to British combatants. Perhaps the most unusual action of this fresh war took place on the other side of the Atlantic Ocean against an enemy that wasn't even human.
In December 1654, Cromwell, seeking commercial gain, sent Lieutenant-Colonel Robert Venables to attack the Spanish possessions in the Caribbean. The expedition was poorly timed, shoddily organised, and featured a command that was split between Venables, who would lead the land campaign, and General at Sea William Penn (the father of the founder of Pennsylvania), who would lead the fleet. Quarreling immediately broke out upon their arrival in Barbados in January 1655. Cromwell had given the expedition free reign to attack as and where it thought best, but Venables was nervous about assaulting the well-defended wealthy Spanish settlements due to the poor discipline of his men and their lack of sufficient equipment and provisions. Finally the two men compromised and decided to attack the island of Hispaniola, 800 miles to the northwest, home to the city of San Domingo.
Things immediately started going sour. Torrential rains rotted the food and ruined the gunpowder. In addition the expedition hadn't brought any containers with which to store water and so could not even collect the rain for drinking. At this point the Venables-Penn relationship was so bad that the lieutenant-colonel thought the admiral would maroon him as soon as they reached Hispaniola. When they did indeed reach the island the force of 3,000 marines landed some forty miles from San Domingo and began marching through the dense jungle. The Spanish, who had plenty of warning of their approach, ambushed them twice along the way. Having made little progress, one night whilst in camp the British heard movement in the jungle around them and became convinced that the Spanish had surrounded them. The next day the nervous Venables ordered a withdrawl back to the ships and Penn took the entire force off of the island.
However, the Spanish accounts tell of no army in proximity of the British force that night. Instead the rustling in the forest undergrowth that had terrified the British marines was actually thousands of fiddler crabs migrating. This army of crustaceans had effectively defeated the expedition simply by scuttling through the jungle at the right time.
On the return voyage to England Venables's force did manage to take the thinly defended island of Jamaica. There the expedition founded the settlement of Port Cagway, which, ironically for a Commonwealth settlement, would go on to become Port Royal. This could only have served as a small consolation to the disgraced Venables and Penn, who both served a term in the Tower of London upon their return to England. The crabs had won an absolute victory.
for the story of another of the British army's defeats by a non human foe, please see